The present invention relates to the cooling and damping of rotor blades and stationary vanes (both of which are generically referred to herein as xe2x80x9cbladesxe2x80x9d unless otherwise indicated). The invention relates more particularly to cooling and damping of blades using a coolant supplied to internal channels in the blades that are lined with a shape memory alloy, or superelastic alloy (both of which are hereinafter generally referred to as a xe2x80x9cshape memory alloyxe2x80x9d).
Compressors and turbines are examples of the turbo-machinery that include a number of rotor blades that are driven in a rotational sense by a gas passing therethrough. For example, a turbine produces rotational power by receiving high-temperature, high-pressure gases such as combustion gases from a fuel combustor, and expanding the gases to a lower temperature and lower pressure via an alternating series of stationary vanes and rotating blades. A gas turbine may have a single xe2x80x9cstagexe2x80x9d consisting of a row of stationary vanes followed by a row of rotor blades, or it may have two or more such stages in series.
In high-performance gas turbine engines, the temperature of the combustion gases entering the first stage of the turbine typically is so high that the available materials for constructing the stationary vanes and rotor blades are not capable of withstanding the extreme temperature without some type of active cooling of the blades and vanes. Thus, modem advances in gas turbine technology have largely been made through discoveries of improved materials capable of withstanding higher temperatures, coupled with improved cooling schemes. These cooling schemes have included film cooling techniques and the circulation of coolant through internal passages defined by a turbine blade as described in more detail by U.S. patent application Ser. No. 10/029,451 entitled Fluid-Cooled Turbine Blades by James Lobitz, et al. filed Dec. 19, 2001; the contents of which are incorporated herein in their entirety.
The blades of compressors, turbines and other turbo-machinery oftentimes also disadvantageously vibrate during operation. These vibrations are primarily due to disturbances in the working fluid and the relatively high rotational speeds at which these machines operate. Among other things, blade vibration may shorten the life and reduce the operating range, including the maximum rotational speed, of a compressor, turbine or other turbo-machinery. In order to improve the efficiency with which compressors, turbines and other turbo-machinery operate and to permit the rotational speeds of these turbo-machines to be further increased, it is desirable to reduce the vibration of the blades. As such, several techniques have been developed to at least partially damp blade vibration.
One device intended to reduce blade vibration applies friction at the tips of the blades. Unfortunately, these damping devices include a large number of components which increase the cost and complexity of the damping devices. In addition, these damping devices or components thereof may possibly become separated from the blades, thus creating the risk of foreign object damage to the blades and/or other portions of the compressor, turbine or other turbo-machinery incorporating these damping devices.
Another damping technique employs annular vibration, or shock, absorbers formed of shape memory alloys that are disposed proximate the base or root of the blade. Since the vibrations are generally more pronounced proximate the tips of the blades, however, the annular vibration, or shock, absorbers placed near the base or root of the blades may not damp the vibrations as efficiently as desired.
Accordingly, although various techniques have been developed to damp blade vibrations, it would be desirable to improve the damping of blade vibrations in order to increase the life and operating range, including rotational speeds, of turbines, compressors and other turbo-machinery.
The present invention addresses the above needs and achieves other advantages, by providing a damped blade (either a rotor blade or a stationary vane of a compressor, turbine or other turbo-machinery) that comprises a blade structural member defining at least one coolant channel and a liner formed of a shape memory alloy extending at least partially along the at least one coolant channel defined by the blade structural member. The shape memory alloy that forms the liner is preferably maintained generally at its transition temperature by means of coolant circulated through the at least one coolant channel. As such, the shape memory alloy that forms the liner will resist the onset of vibrations within the blade, thereby effectively damping blade vibrations.
The blade structural member generally extends along a blade longitudinal axis from an inner end to an outer end. In one advantageous embodiment, the blade structural member defines the coolant channel to be formed of first and second legs. The first and second legs are in fluid communication such that coolant passes from the first leg into the second leg during operation. In this embodiment, the first leg extends longitundally from the inner end of the blade structural member to a location proximate the outer end of the blade structural member. The second leg, in turn, is connected to the first leg at the location proximate the outer end of the blade structural member and returns to the inner end of the blade structural member. In this embodiment, the liner may also include first and second portions that extend at least partially along the first and second legs, respectively. Preferably, the first portion of the liner is formed of a shape memory alloy having a transition temperature that is lower than the transition temperature of the shape memory alloy that forms the second portion of the liner. As such, the coolant can maintain the shape memory alloy that forms the liner at approximately its transition temperature even as the coolant is heated during its passage through the coolant channel.
In addition, the first leg may be proximate to the pressure side of the blade and the second leg may be proximate to the other surface of the blade (e.g. the suction side of the blade). Thus, the liner of the first leg is positioned to absorb the compressive force generated by the blade vibrating toward the first leg, while the liner of the second leg is positioned to absorb the corresponding tensile force.
Other than the coolant channel(s) defined by the blade structural member, the blade structural member is preferably solid. Additionally, the damped blade of the present invention is preferably designed to enhance the load transfer path between the blade structural member and the liner formed of a shape memory alloy in order to insure effective transfer of the compressive and tensile forces created in the blade structural member by the onset of blade vibration and to correspondingly enhance the vibrational damping. Typically, the liner is in contact with the material forming the blade structural member along the entire length of the coolant channel. In order to enhance the load transfer path, the liner of one embodiment may have a roughened exterior surface. In addition or in the alternative, the liner may define a circumferential groove on the exterior surface of the liner. While the circumferential groove may extend in various manners about the exterior surface as the liner, the liner of one embodiment defines the circumferential groove to extend helically in a longitudinal direction. In the alternative, a raised land may extend circumferentially around the exterior of the liner to enhance the load transfer.
The damped blade may be incorporated in a blade damping system according to one aspect of the present invention. In this regard, the blade damping system not only includes the blade, including the blade structural member defining at least one coolant channel and a liner formed of a shape memory alloy extending at least partially along the at least one coolant channel, but also a heat exchanger. The heat exchanger is in fluid communication with the at least one coolant channel. As such, the heat exchanger extracts heat from coolant following passage of the coolant through the at least one coolant channel. The heat exchanger then redirects or returns the coolant to the at least one coolant channel.
Advantageously, the heat exchanger serves to maintain the coolant at a temperature having a predetermined relationship with respect to a predefined transition temperature of the shape memory alloy that forms the liner. Shape memory alloys exhibit several transition temperatures with the temperature of the coolant having a predetermined relationship with respect to any one or more of the transition temperatures. The transition temperatures include the Af temperature, the Ap temperature, the As temperature, the Mf temperature, the Mp temperature and the Ms temperature.
In this regard, the heat exchanger is generally adapted to maintain the coolant in a range from just below the Af temperature of the shape memory alloy to 50 degrees C. above the Af temperature, thereby facilitating the vibration damping by the shape memory alloy that forms the liner. In the alternative, the coolant temperature may be maintained between the Mp and Ap temperatures or between the Mf and Af temperatures of the shape memory alloy. Other ranges, defined with respect to the various transition temperatures are encompassed by the invention.
The blade of the present invention may be fabricated in various manners. According to another aspect of the present invention, however, a method of fabricating the blade is provided in which a prefabricated liner, typically having a first leg and a second leg, and formed of a shape memory alloy is positioned within a mold that defines the shape of the resulting blade. The mold is then filled with an at least partially molten blade material that has a lower melting temperature than the shape memory alloy.
For example, the liner may be made of the shape memory alloy Nitinol and the mold may be filled with molten aluminum. In this example the aluminum has a lower melting temperature than Nitinol. Advantageously, the melting point of aluminum alloys, generally 650 degrees C., happens to be well within the heat treating temperature range for Nitinol, generally 500 to 800 degrees C. Thus, the molding of the aluminum blade may be tailored to simultaneously perform the heat treatment of the Nitinol liner. By combining the blade molding operation with the liner heat treatment, an energy savings may be realized.
Regardless of the blade material, the blade material at least partially surrounds the liner formed of a shape memory alloy. The blade material is then permitted to at least partially solidify prior to removing the mold to thereby produce the blade having the liner formed of a shape memory alloy at least partially embedded therein.
In one embodiment, the liner is filled with a liquid that boils at a lower temperature than the melting temperature of the blade material prior to filling the mold with the at least partially molten blade material. For example, the liner may be filled with water prior to introducing the at least partially molten blade material. Upon the introduction of the at least partially molten blade material, the liquid boils off to somewhat cool the liner formed of a shape memory alloy and to create a slight compressive fit of the cooled, solidified blade material about the liner. In the alternative, the liner may be left empty and allowed to heat during the molding of the blade in order to heat treat the shape memory alloy of the liner, as discussed previously. Upon completion of the heat treatment, the liquid may then be rapidly introduced into the liner to quench the shape memory alloy liner. Another embodiment includes continuously flowing liquid through the liner to provide quenching and/or continuous cooling through the blade molding operation.
Accordingly, a blade is provided according to the present invention that effectively damps vibrations. In addition, the blade of at least some embodiments is cooled concurrent with the vibration damping. As a result of the vibration damping and cooling, the blade of the present invention may increase the life and operating range of a compressor, turbine or other turbo-machinery.